Catalytically active particulate filter with high filtration efficiency

Abstract

The invention relates to a wall-flow filter for removing particles from the exhaust gas of an internal combustion engine, comprising a wall-flow filter substrate of length L and a coating Z and F which differ from one another, wherein the wall-flow filter substrate has channels E and A which run parallel between a first end and a second end of the wall-flow filter substrate, are separated by a porous wall and form surfaces O E and O A respectively, and wherein the channels E are closed at the second end and the channels A are closed at the first end, and wherein the coating Z is located in the porous wall and / or on the surface O A but not on the surface O E and comprises palladium and / or rhodium, cerium / zirconium mixed oxide, characterized in that the coating F is located in the porous wall and / or on the surface O E but not on the surface O A and comprises a particulate metal compound and is free of noble metals.

Description

[0001] This invention relates to a wall-flow filter, its manufacturing method, and its use in reducing harmful exhaust gases from internal combustion engines.

[0002] Diesel particulate filters or gasoline particulate filters, with and without additional catalytically active coatings, are suitable aggregates for removing particulate emissions and reducing harmful substances in exhaust gases. These are wall-flow honeycomb structures, referred to as catalyst supports, carriers, or substrate monoliths. To meet legal standards, current and future applications for exhaust aftertreatment of internal combustion engines are expected to combine particulate filters with other catalytically active functions, not only for cost reasons but also for installation space reasons. Catalytically active coatings can be positioned on a surface or in the walls of channels forming that surface. The catalytically active coating is typically applied to the catalyst support in the form of a suspension during a so-called coating operation. Automotive exhaust catalyst manufacturers have published numerous such methods in the past; see, for example, EP1064094B1, EP2521618B1, WO10015573A2, EP1136462B1, US6478874B1, US4609563A, WO9947260A1, JP5378659B2, EP2415522A1, and JP2014205108A2.

[0003] Compared to a flow-through support of the same size, using a particulate filter (with or without catalytic coating) results in a significant increase in exhaust back pressure, leading to a decrease in engine torque or potentially increased fuel consumption. To avoid even further increasing exhaust back pressure, the amount of catalytically active precious metal oxide support material or catalytically active catalyst material is typically applied in smaller quantities in the case of a filter than in the case of a flow-through support. Therefore, the catalytic effect of a catalytically coated particulate filter is often inferior to that of a flow-through support of the same size.

[0004] Efforts have been made to provide particulate filters that exhibit good catalytic activity due to the active coating while still maintaining the lowest possible exhaust back pressure. Regarding low exhaust back pressure, it has proven advantageous that the catalytically active coating is not present as a layer on the channel walls of a porous wall-flow filter, but rather that the catalytically active material is dispersed within the filter's channel walls; see, for example, WO2005016497A1, JPH01-151706, and EP1789190B1. For this purpose, the particle size of the catalytic coating is chosen such that the particles penetrate into the pores of the wall-flow filter and can be immobilized there by calcination. A disadvantage of catalytically active filters with an internal wall coating is that the amount of catalytically active material is limited by the absorption capacity of the porous walls.

[0005] It has been found that increasing the conversion of harmful substances in exhaust gases can be achieved by applying catalytically active materials to the surface of the channel walls of wall-flow honeycomb structures. Combinations of upper and lower wall coatings with catalytically active materials are also possible, thus allowing for further improvement in catalytic performance without significantly increasing back pressure.

[0006] Besides catalytic effects, another function of filters that can be improved by coatings is their filtration efficiency, i.e., the filtration effect itself. WO 2011151711A1 describes a method in which a dry aerosol is agitated onto an uncoated or catalytically coated filter, the filter carrying a catalytically active material (an in-wall coating with a carrier coating) within the channel walls. The aerosol is provided by distributing powdered high-melting-point metal oxides, and the aerosol is guided through the inlet side of the wall-flow filter by means of an airflow. In this case, individual particles with a particle size of 0.2 μm to 5 μm agglomerate to form a bridging network of particles and are deposited as a layer on the surface of individual inlet channels through the wall-flow filter. Typical powder loadings for the filter are between 5 g and 50 g per liter of filter volume. It is explicitly stated that it is undesirable to obtain a coating with metal oxides inside the pores of the wall-flow filter.

[0007] Another method for increasing the filtration efficiency of non-catalytically active filters is described in WO2012030534A1. In this case, a filter layer (“recognition layer”) is formed on the wall of the flow channel on the inlet side by depositing ceramic microparticles via microparticle aerosol. This layer consists of oxides of zirconium, aluminum, or silicon, preferably in the form of fibers with a length in the range of 1 nm to 5 μm, and has a layer thickness greater than 10 μm, typically 25 μm to 75 μm. After the coating process, the applied powder microparticles are calcined during a thermal process.

[0008] Another method is described in patent specification US8277880B2, in which a film (“trapping layer”) is formed on the surface of the filter inlet channel to increase the filtration efficiency of a non-catalytically active wall-flow filter. The filter film is formed on the surface of the inlet channel by drawing an airflow loaded with ceramic particles (e.g., silicon carbide or cordierite) through the inlet channel. After applying the filter layer, the honeycomb structure is calcined at a temperature above 1000°C to increase the adhesion strength of the powder layer to the channel wall. EP2502661A2 and EP2502662B1 mention additional wall coatings applied by powder.

[0009] US8388721B2 describes coating the interior of the pores of a wall-flow filter substrate by spray-drying particles. However, in this case, the powder should penetrate deeply into the pores. 20% to 60% of the wall surface should remain accessible to the dust particles, thus keeping it open. The powder gradient, which may be more or less steep, between the inlet and outlet sides can be adjusted depending on the flow rate of the powder / gas mixture. According to US8388721B2, the pores of the filter channel walls coated with powder can then be coated with a catalytically active component. Here, the catalytically active material is also located within the filter channel walls.

[0010] EP2727640A1 also describes, for example, introducing powder into the pores using an aerosol generator. Here, a non-catalytically coated wall-flow filter is coated in a manner using an airflow containing, for example, alumina particles, such that intact particles with a particle size of 0.1 μm to 5 μm are deposited as porous packing material in the pores of the wall-flow filter. In addition to filtration, the particles themselves also perform other functions of the filter. For example, based on the filter volume, these particles are deposited in the pores of the filter at a rate greater than 80 g / L. The particles fill 10% to 50% of the volume of the pores in the channel walls. This filter, both with and without smoke, exhibits improved filtration efficiency compared to an untreated filter, and also has the lower exhaust back pressure of a filter with smoke.

[0011] In WO2018115900A1, the wall-flow filter is optionally coated with dried synthetic ash, thereby forming a continuous membrane layer on the wall of the optionally catalytically coated wall-flow filter.

[0012] The purpose of all the prior art patents listed above is to improve the filtration efficiency of filters by powder coating. Filters optimized in this way may also carry a catalytically active coating in the porous channel walls before powder coating. However, none of the examples show the simultaneous achievement of optimized filter catalytic effect and improved filtration efficiency.

[0013] Therefore, there remains a need for particulate filters that optimize both catalytic activity and filtration efficiency relative to exhaust gas back pressure. The object of this invention is to provide a corresponding particulate filter that combines sufficient filtration efficiency with the lowest possible increase in exhaust gas back pressure and high catalytic activity.

[0014] These and other objectives, which are obvious from the prior art, are achieved by the particulate filter according to claims 1 to 14. Claim 15 relates to the preparation of a particulate filter according to the invention. Claim 16 relates to the use of a particulate filter for the aftertreatment of exhaust gases from internal combustion engines.

[0015] This invention relates to a wall-flow filter for removing particulate matter from exhaust gases of an internal combustion engine. The wall-flow filter comprises a wall-flow filter substrate of length L and coatings Z and F that are different from each other.

[0016] The wall-flow filter substrate has channels E and A, which extend parallel between a first end and a second end of the wall-flow filter substrate, are separated by porous walls, and respectively form surface O. E and O A And wherein the channel E is closed at the second end and the channel A is closed at the first end, and

[0017] The coating Z is located in the porous wall and / or on the surface O. A On, but not on surface O E Above, and contains palladium and / or rhodium as well as cerium / zirconium mixed oxide,

[0018] The coating F is characterized in that it is located in the porous wall and / or on the surface O. E On, but not on surface O A It contains particulate metal compounds but no precious metals.

[0019] In the intended use of the wall-flow filter according to the invention for cleaning internal combustion engine exhaust gases, the exhaust gases flow into the filter at one end and exit the filter again at the other end after passing through a porous wall. Thus, for example, if the exhaust gases enter the filter at the first end, channel E represents the inlet channel or inflow-side channel. After passing through the porous wall, it then exits the filter at the second end, such that channel A represents the outlet channel or outflow-side channel.

[0020] All known ceramic wall-flow filter substrates commonly used in automotive exhaust catalysis can be used as wall-flow filter substrates. Porous wall-flow filter substrates made of cordierite, silicon carbide, or aluminum titanate are preferred. These wall-flow filter substrates have channels E and A, which, as described above, act as inlet channels (also referred to as inflow channels) and outlet channels (also referred to as outflow channels). The outflow-side ends of the inflow channel and the inflow-side ends of the outflow channel are offset and sealed to each other by a generally airtight "plug". In this configuration, the exhaust gas to be purified and flowing through the filter substrate is forced through the porous wall between the inflow and outflow channels, resulting in particulate filtration. The particulate filtration performance can be designed using porosity, pore / radius distribution, and wall thickness. According to the invention, the porosity of the uncoated wall-flow filter substrate is typically greater than 40%, for example, 40% to 75%, particularly 50% to 70% [measured according to the latest version of DIN 66133, date of application]. The average pore diameter d of the uncoated wall-flow filter substrate... 50The pore size distribution of the wall-flow filter substrate is at least 7 μm, for example, from 7 μm to 34 μm, preferably greater than 10 μm, particularly more preferably from 10 μm to 25 μm, or most preferably from 15 μm to 20 μm [measured according to the latest version of DIN 66134 as of the application date], wherein the d 50 The value is understood to refer to 50% of the total pore volume that can be determined by mercury intrusion porosimetry, specified by a diameter less than or equal to d. 50 The value of pore formation. In the case of the wall-flow filter according to the invention, the wall-flow filter substrate having coatings Z and F and optionally coating Y (see below) particularly preferably has a pore size d of 10 μm to 20 μm. 50 And a porosity of 50% to 65%.

[0021] Those skilled in the art will know that, because the plugs close channels E and A in an offset manner, the entire length L of the wall-flow filter substrate may be unavailable for coating. For example, channel E is closed at the second end of the wall-flow filter substrate, making the surface O available for coating... E Therefore, it can be slightly smaller than the length L. Of course, this only applies if the coating exists at or slightly below 100% of the length L. In these cases, for simplicity, the following will still refer to 100% of the length L.

[0022] If the coating Z is located on the surface O of the wall flow filter substrate A The upper part preferably extends from the second end of the wall flow filter substrate to 50% to 90% of the length L.

[0023] Surface O A The coating on top is what's called a wall coating. This means the coating rises to the surface O. A The material enters channel A of the wall-flow filter substrate, thereby reducing the channel cross-section. In this embodiment, it interacts with surface O. A The pores of adjacent porous walls are filled with coating Z only to a small extent. More than 80%, preferably more than 90%, of coating Z is not located in the porous walls.

[0024] The coating on the wall extends above the wall surface to a certain height. However, the thickness of layers Z and Y is typically from 5 μm to 250 μm, preferably from 7.5 μm to 225 μm, and most preferably from 10 μm to 200 μm, wherein the thickness of this layer is preferably determined in the middle of the web of the corresponding channel rather than at the corner. Standard analytical methods (such as scanning electron microscopy) known to those skilled in the art are suitable for determining the layer thickness.

[0025] If the coating Z is located in the porous wall of the wall-flow filter substrate, it preferably extends from the first end of the wall-flow filter substrate to 50% to 100% of the length L.

[0026] The coating in the porous wall is a so-called in-wall coating. In this embodiment, the surface O adjacent to the porous wall... A Coating Z is applied only to a small extent.

[0027] Measured from the second end of the wall-flow filter substrate, the minimum length of the coating Z is at least 1.25 cm, preferably at least 2.0 cm, and most preferably at least 2.5 cm.

[0028] The coating Z can have a thickness gradient along the length L, such that the thickness of the coating Z increases from the second end to the first end along the length L of the wall-flow filter. In this case, the thickness of the coating at one end is preferably more than twice the thickness at the other end, more preferably at most three times. In this case, the thickness is the thickness of the coating Z rising to the surface O. A The thickness gradient of the coating on the channel walls also allows for adjustment of the filtration efficiency along the entire length L of the filter. The result is more uniform deposition of soot across the entire filter wall, leading to increased exhaust back pressure and potentially better soot combustion.

[0029] However, the coating Z can also have a thickness gradient along the length L, such that the thickness of the coating Z decreases from the second end to the first end along the length L of the wall-flow filter. In this case, the thickness of the coating at one end can preferably be more than twice the thickness at the other end, more preferably at most three times. In this case, the thickness is the thickness of the coating Z rising to the surface O. A The thickness gradient of the coating on the channel walls also allows for adjustment of the filtration efficiency along the entire length L of the filter. The result is more uniform deposition of soot across the entire filter wall, leading to increased exhaust back pressure and potentially better soot combustion.

[0030] Coating Z is a catalytically active coating, particularly due to its components palladium and / or rhodium. In the context of this invention, "catalytically active" should be understood to mean the ability to convert harmful exhaust gas components from an internal combustion engine into less harmful exhaust gas components. Specifically, exhaust gas component NO should be mentioned here. x CO and HC. Therefore, coating Z is particularly preferably ternary catalytically active, especially at operating temperatures from 250°C to 1100°C.

[0031] Coating Z contains the noble metals palladium and / or rhodium, wherein platinum is also present as an additional noble metal only in exceptional cases. Particularly preferably, coating Z contains palladium and rhodium but does not contain platinum.

[0032] In another embodiment, coating Z contains the precious metals platinum and / or rhodium, wherein palladium is also present as an additional precious metal only in exceptional cases.

[0033] In another embodiment, coating Z contains the noble metals platinum and palladium, and optionally rhodium. In this embodiment, it is advantageous that the mass ratio of platinum to palladium is 15:1 to 1:15, particularly 10:1 to 1:10.

[0034] Based on the particulate filter according to the invention, the proportion of rhodium in the total precious metal content is particularly greater than or equal to 5% by weight, preferably greater than or equal to 10% by weight. For example, the proportion of rhodium in the total precious metal content is from 5% to 20% by weight or from 5% to 15% by weight. Based on the volume of the wall-flow filter substrate, the amount of precious metal used is typically from 0.10 g / L to 5 g / L.

[0035] Precious metals are typically fixed to one or more carrier materials.

[0036] All materials used for this purpose that are familiar to those skilled in the art are considered supporting materials. Specifically, such materials are BET materials with a surface area of ​​30 m². 2 / g to 250m 2 / g, preferably 100m 2 / g to 200m 2 / g (determined according to the latest version of DIN 66132 as of the application date) of metal oxide. Particularly suitable carrier materials for precious metals are selected from the series consisting of: alumina, doped alumina, silicon oxide, titanium dioxide, and mixed oxides of one or more of these. Doped alumina is, for example, alumina doped with lanthanum oxide, zirconium oxide, barium oxide, and / or titanium oxide. Advantageously, alumina or lanthanum-stabilized alumina is used, wherein in each case, the amount of lanthanum is 1% to 10% by weight, preferably 3% to 6% by weight, calculated as La2O3 and based on the weight of the stabilized alumina.

[0037] Similarly, in the case of alumina doped with barium oxide, the proportion of barium oxide is particularly 1% to 10% by weight, preferably 3% to 6% by weight, calculated in BaO and based on the weight of stable alumina in each case.

[0038] Another suitable support material is lanthanum-stabilized alumina, with its surface coated with lanthanum oxide, barium oxide, and / or strontium oxide.

[0039] The coating Z preferably contains at least one type of alumina or doped alumina.

[0040] Coating Z contains at least one cerium / zirconium mixed oxide as an oxygen storage component. The mass ratio of cerium oxide to zirconium oxide in these products can vary over a wide range. This ratio is, for example, 0.1 to 1.5, preferably 0.15 to 1 or 0.2 to 0.9.

[0041] Preferred cerium / zirconium mixed oxides contain one or more rare earth metal oxides and are therefore referred to as cerium / zirconium / rare earth metal mixed oxides. Within the meaning of this invention, the term "cerium-zirconium-rare earth metal mixed oxide" does not include physical mixtures of cerium oxide, zirconium oxide, and rare earth oxides. Instead, "cerium / zirconium / rare earth metal mixed oxide" is characterized by a generally homogeneous three-dimensional crystal structure that ideally does not contain a phase (fixing liquid) of pure cerium oxide, zirconium oxide, or rare earth oxides. However, depending on the manufacturing process, imperfectly homogeneous products may be produced, which are generally usable without defects. This also applies to cerium / zirconium mixed oxides that do not contain any rare earth metal oxides. In all other respects, the terms "rare earth metal" or "rare earth metal oxide" within the meaning of this invention do not include cerium or cerium oxide.

[0042] Lanthanum oxide, yttrium oxide, praseodymium oxide, neodymium oxide, and / or samarium oxide can be considered, for example, as rare earth metal oxides in cerium-zirconium-rare earth metal mixed oxides. Lanthanum oxide, yttrium oxide, and / or praseodymium oxide are preferred. Lanthanum oxide and / or yttrium oxide are particularly preferred, and more particularly preferred are lanthanum oxide and yttrium oxide, yttrium oxide and praseodymium oxide, and lanthanum oxide and praseodymium oxide. In embodiments of the invention, the oxygen storage component does not contain neodymium oxide.

[0043] Based on cerium / zirconium / rare earth metal mixed oxides, the proportion of rare earth metal oxides in the cerium / zirconium / rare earth metal mixed oxides is particularly 3% to 20% by weight.

[0044] If the cerium / zirconium / rare earth metal mixed oxide contains yttrium oxide as a rare earth metal, then the proportion based on the cerium / zirconium / rare earth metal mixed oxide is preferably 4% to 15% by weight. If the cerium / zirconium / rare earth metal mixed oxide contains praseodymium oxide as a rare earth metal, then the proportion based on the cerium / zirconium / rare earth metal mixed oxide is preferably 2% to 10% by weight. If the cerium / zirconium / rare earth metal mixed oxide contains lanthanum oxide and other rare earth oxides as rare earth metals, such as yttrium oxide or praseodymium oxide, the mass ratio is particularly 0.1 to 1.25, preferably 0.1 to 1.

[0045] Based on the volume of the wall-flow filter substrate, coating Z typically contains 15 g / L to 120 g / L of oxygen storage component. The mass ratio of carrier material to oxygen storage component in coating Z is typically 0.25 to 1.5, for example, 0.3 to 1.3.

[0046] For example, the total mass ratio of all alumina (including doped alumina) in coating Z to the total mass ratio of all cerium / zirconium mixed oxides is 10:90 to 75:25.

[0047] In embodiments of the present invention, coating Z comprises lanthanum-stabilized alumina, rhodium, palladium or palladium and rhodium, and a cerium / zirconium / rare earth metal mixed oxide containing yttrium oxide and lanthanum oxide as rare earth metal oxides.

[0048] In other embodiments of the invention, coating Z comprises lanthanum-stabilized alumina, rhodium, palladium or palladium and rhodium, and a cerium / zirconium / rare earth metal mixed oxide containing praseodymium oxide and lanthanum oxide as rare earth metal oxides.

[0049] In other embodiments of the invention, coating Z comprises lanthanum-stabilized alumina, rhodium, palladium, or palladium and rhodium, a cerium / zirconium / rare earth metal mixed oxide containing praseodymium oxide and lanthanum oxide as rare earth metal oxides, and a second cerium / zirconium / rare earth metal mixed oxide containing yttrium oxide and lanthanum oxide as rare earth metal oxides.

[0050] The coating Z preferably does not contain zeolite or molecular sieve.

[0051] If coating Z contains alumina or doped alumina, the weight ratio of the total mass of all alumina or doped alumina to the total mass of all cerium / zirconium mixed oxides or cerium / zirconium / rare earth metal mixed oxides is specifically 10:90 to 75:25.

[0052] According to the present invention, coating F comprises particulate metal compounds and does not contain noble metals. Therefore, it is not catalytically active within the meaning of this invention, i.e., it cannot oxidize the waste gas components CO and HC and reduce NO. x .

[0053] Preferably, the coating F consists of one or more particulate metal compounds, i.e., it does not contain any other components.

[0054] Suitable metal compounds are well known to those skilled in the art because they are typically high-melting-point metal compounds commonly used as carrier materials for catalysts in automotive exhaust systems. Preferred are metal oxides, metal sulfates, metal phosphates, metal carbonates, or metal hydroxides, or mixtures thereof. Metal oxides are particularly preferred.

[0055] The metal oxides that can be considered are primary, binary or ternary metal oxides or mixtures thereof.

[0056] The metals considered are specifically selected from alkali metals, alkaline earth metals, earth metals, and transition metals. Preferably, the metals are selected from the group consisting of: calcium, potassium, magnesium, strontium, barium, iron, zinc, aluminum, silicon, titanium, zirconium, lanthanum, praseodymium, bismuth, cobalt, nickel, copper, and cerium.

[0057] Very particularly preferred metal compounds are cerium oxide, titanium dioxide, zirconium dioxide, silicon dioxide, aluminum oxide, or mixtures or mixed oxides thereof.

[0058] Alternatively, so-called pyrolytic metal oxides can also be used. Generally speaking, the metal oxides produced by pyrolysis should be understood as metal oxide powders obtained through flame hydrolysis or flame oxidation of metal oxide precursors in a hydrogen-oxygen gas flame. https: / / de.wikipedia.org / w / index.php?title=Pyrogenes_Siliciumdioxid&oldid ＝182147815 ;Pater Albers et al., Chemie in unserer Zeit [Chemistry in our Time], 2016, 50, 162–171; Hans Ferkel et al., MTZ–Motortechnische Zeitschrift [EngineTechnology Magazine], 2010, 71, 128–133). These metal oxide powders possess the properties described in the following references for flame-synthesized particulate products: Gutsch et al., (2002) KONA (No. 20); Li S. et al., (2016) Progress in Energy and Combustion Science (Vol. 55); Ulrich G. (1971) Combustion Science and Technology (Vol. 4). Pyrolytic metal oxides are typically characterized by high specific surface area and low bulk density. Generally, this method can be used to prepare large surface area oxides of various metals. Such oxides are advantageously made from a group of metals including silicon, aluminum, titanium, zirconium, cerium, or mixtures of such metals.

[0059] The wall-flow filter according to the invention has a coating F with an increasing concentration gradient from its first end to its second end in the longitudinal direction of the filter. According to the invention, the term "increasing gradient" means that the concentration gradient of the coating F in the filter increases axially from one end to the other, possibly from a negative value to a positive value.

[0060] In the intended use of the wall-flow filter (where exhaust gas flows in at its first end and flows out at its second end), a larger amount of coating F is preferably located near the second end of the wall-flow filter substrate, while a significantly smaller amount of coating F is located near the first end of the wall-flow filter substrate.

[0061] Simulations of gas flow in a wall-flow filter show that the rear third of the substrate is primarily (greater than 50%) responsible for the overall filtration performance of the filter. The increased application of coating F in the rear third of the filter further increases the back pressure there due to lower permeability and a greater diversion of flow to the first two-thirds of the filter. Therefore, the filter should have a gradient of coating F that increases more rapidly from the first end to the second end to enhance its filtration efficiency.

[0062] This allows for necessary modifications to adjust for favorable exhaust back pressure. In another embodiment of the invention, the concentration gradient of coating F thus increases less abruptly from the first end to the second end, or the concentration gradient of coating F decreases.

[0063] The coating F is preferably located within the porous wall of the wall-flow filter substrate, which means that the particle size of the metal compound must be suitable for the pore size of the wall-flow filter substrate. Therefore, the particles of the metal compound have a particularly defined particle size distribution.

[0064] Because wall-flow filter substrates typically contain pores of varying sizes, it is ideal for large pores to contain a certain proportion of larger particles and for small pores to contain a certain proportion of smaller particles. This means that the metal compound preferably has a multi-peak or broad q3 particle size distribution.

[0065] The definition of particle size or particle size distribution of metal compounds is distinguished between number-dependent (q0) and volume-dependent (q3) particle size distributions, depending on the method of determining the number of particles and other factors (M. Stieβ, Mechanische Verfahrenstechnik-Partikeltechnologie 1 (Mechanical Process Technology-Particle Technology 1), Springer, 3rd edition, 2009, p. 29).

[0066] Here, the coarse particle size of the metal compound (defined by the d90 value of the q3 particle size distribution, measured using a Beckman Tornado drying dispersion module according to the latest ISO 13320-1 of the application date) should be less than or equal to 60% of the average volume-related q3 pore size (d50) of the filter used (measured according to the latest version of DIN 66134 of the application date), preferably less than 50%. The average q3 particle size (d50) of the metal compound should be 5% to 30% of the average q3 pore size (d50) of the filter used, preferably 7% to 25%, and very preferably 10% to 25%. The d10 value of the q3 particle size distribution of the metal compound (which describes the fine particle size) should be 20% to 60% of the average q3 particle size (d50) of the metal compound, preferably 25% to 50%, and particularly preferably 25% to 40%. The d10 value of the quantity-related q0 particle size distribution should generally be higher than 0.05 μm, preferably higher than 0.08 μm, and particularly preferably higher than 0.1 μm.

[0067] Based on the external filtration volume in liters, the particles of metal compounds particularly have a particle size greater than 5m. 2 / l, preferably greater than 10m 2 / l and very specifically preferred to be greater than 15m 2 / l total surface area.

[0068] The total surface area of ​​the particles (SV) is obtained from the particle size x according to the following formula:

[0069]

[0070] (M. Stieβ, Mechanical Process Engineering - Particle Technology 1, Springer, 3rd ed., 2009, p. 35), and thereby obtains a mass-dependent surface (M. Stieβ, Mechanical Process Engineering - Particle Technology 1, Springer, 3rd ed., 2009, p. 16), in which the density of the particles is ρ:

[0071]

[0072] ou+ersurfaceofthepowderS outer [m 8 ] = S m ·m po9der

[0073] Those skilled in the art can readily determine the particle size distribution and total surface area of ​​the metal compounds in the finished wall-flow filter according to the invention by washing the metal compounds out of the wall-flow filter substrate with water. He / she simply collects the washed material, dries it, and then determines the desired parameters using methods known to him / her or described above.

[0074] In particular, as a result of the manufacturing process, a portion of the coating F can also be formed on surface O. E Above. Specifically, 1% to 90% of the total mass of coating F, but preferably 2% to 70%, and particularly preferably 3% to 50%, may be located on surface O. E superior.

[0075] Coating F is preferably not on surface O E Instead of forming a coherent continuous layer, it selectively blocks the large pores of the wall-flow substrate, resulting in island-like deposition patterns.

[0076] Coating F may exist entirely or partially as a sealing layer on surface O. E Above. In this case, the thickness of coating F is typically 1 μm to 75 μm, but preferably 5 μm to 65 μm.

[0077] In which coating Z is located on surface O A According to an embodiment of the invention, the thickness of coating F is less than or equal to the thickness of coating Z. The ratio of the thickness of coating F to the thickness of coating Z is preferably 0.1 to 1, more preferably 0.15 to 0.95, and particularly preferably 0.2 to 0.9. Furthermore, the average particle size d of the oxide in coating F... 50 The average particle size d of the coating Z is less than or equal to 50 Preferably, the d of the particles of coating F 50 d of the particles of coating Z 50 The ratio is 0.01 to 1, preferably 0.05 to 0.9, and particularly preferably 0.15 to 0.8.

[0078] In an embodiment of the invention, where coating Z is located within pores of the filter wall, the layer thickness of coating F is greater than or equal to the layer thickness of coating Z. Furthermore, the average particle size d of the oxide in coating F... 50 The average particle size d of the coating Z is greater than or equal to the average particle size of the coating Z. 50 Preferably, the d of the particles of coating F 50 d of the particles of coating Z 50 The ratio is 1 to 7, preferably 1.05 to 6, and particularly preferably 1.1 to 5.

[0079] In which coating Y is located on surface O E According to an embodiment of the invention, the thickness of coating F is less than or equal to the thickness of coating Y. The ratio of the thickness of coating F to the thickness of coating Y is preferably 0.1 to 1, more preferably 0.15 to 0.95, and particularly preferably 0.2 to 0.9. Furthermore, the average particle size d of the oxide in coating F is... 50 The average particle size d of the coating Y is less than or equal to 50 Preferably, the d of the particles of coating F 50 d with the particles of coating Y 50 The ratio is 0.01 to 1, preferably 0.05 to 0.9, and particularly preferably 0.15 to 0.8.

[0080] In an embodiment of the invention, where coating Y is located within pores of the filter wall, the layer thickness of coating F is greater than or equal to the layer thickness of coating Y. Furthermore, the average particle size d of the oxide in coating F... 50 The average particle size d of the coating Y is greater than or equal to the average particle size of the coating Y. 50 Preferably, the d of the particles of coating F 50 d with the particles of coating Y 50 The ratio is 1 to 7, preferably 1.05 to 6, and particularly preferably 1.1 to 5.

[0081] Based on the volume of the wall-flow filter substrate, the coating F is present, for example, in an amount of less than 50 g / L, particularly less than 40 g / L. Based on the volume of the wall-flow filter substrate, the coating F is preferably present in an amount of 2.5 g / L to 40 g / L.

[0082] The coating F may extend over the entire length L of the wall-flow filter substrate or only over a portion thereof. For example, the coating F may extend over 10% to 100%, 25% to 80%, or 40% to 60% of the length L.

[0083] In an embodiment of the wall-flow filter according to the invention, the wall-flow filter substrate has a coating Y different from coatings Z and F, which comprises platinum, palladium, or platinum and palladium, is free of rhodium and cerium / zirconium mixed oxides, and is located in the porous wall and / or on the surface O. E On, but not on surface O A Above. Preferably, the coating Y contains platinum and palladium, wherein the mass ratio of platinum to palladium is 25:1 to 1:25, particularly preferably 15:1 to 1:2.

[0084] In coating Y, platinum, palladium, or platinum and palladium are typically fixed to one or more carrier materials.

[0085] All materials used for this purpose that are familiar to those skilled in the art are considered supporting materials. Specifically, such materials are BET materials with a surface area of ​​30 m². 2 / g to 250m 2 / g, preferably 100m 2 / g to 200m 2 / g (determined according to the latest version of DIN 66132 as of the application date) of metal oxide. Particularly suitable support materials are selected from the following series: alumina, doped alumina, silicon oxide, titanium dioxide, and mixed oxides of one or more of these. Doped alumina is, for example, alumina doped with lanthanum oxide, zirconium oxide, barium oxide, and / or titanium oxide. Advantageously, alumina or lanthanum-stabilized alumina is used, wherein in each case, based on La2O3 and the weight of the stabilized alumina, the amount of lanthanum used in the latter case is 1% to 10% by weight, preferably 3% to 6% by weight.

[0086] Similarly, in the case of alumina doped with barium oxide, the proportion of barium oxide is particularly 1% to 10% by weight, preferably 3% to 6% by weight, calculated based on BaO and the weight of stable alumina in each case.

[0087] Another suitable support material is lanthanum-stabilized alumina, with its surface coated with lanthanum oxide, barium oxide, and / or strontium oxide.

[0088] The coating Y preferably contains at least one type of alumina or doped alumina.

[0089] In one embodiment, coating Y is located only on the surface O of the wall-flow filter substrate. E It extends from its first end over a length of 50% to 90% of the length L.

[0090] In another embodiment, the coating Y is located in the porous wall of the wall-flow filter substrate and preferably extends from its first end over a length of 50% to 100% of the length L.

[0091] If coating Y is present, the mass ratio of coating Y to coating Z is preferably 0.05 to 8.5.

[0092] For example, the carrier material of coating Y has a larger pore volume than the carrier material of coating Z. The ratio of the specific surface area of ​​the carrier oxides of coating Y to that of coating Z is preferably 0.5 to 2, particularly 0.7 to 1.5.

[0093] For example, the ratio of the pore volume of the particulate metal compound in coating F to the pore volume of the carrier material in coating Z is preferably 0.01 to 3, particularly 0.05 to 2.5. The ratio of the specific surface area of ​​the particulate metal compound in coating F to the specific surface area of ​​the carrier oxide in coating Z is preferably 0.1 to 4, particularly 0.25 to 3.

[0094] Coatings Z, F and (if present) Y can be arranged in various ways on the wall-flow filter substrate. Figures 1 to 10 This is illustrated by example, where Figures 1 to 4 This relates to a wall-flow filter according to the invention, comprising only coatings Z and F, while... Figures 5 to 10 The wall-flow filter shown according to the invention further includes a coating Y.

[0095] Figure 1 This relates to a wall-flow filter according to the invention, wherein the coating Z is located on surface O. A The coating is located in channel A and extends for 50% of the length L from the second end of the wall-flow filter substrate. The coating F is located in channel E and extends for the entire length L.

[0096] Figure 2 Also relating to a wall-flow filter according to the invention, wherein the coating Z is located on surface O A In channel A. However, starting from the second end of the wall-flow filter substrate, it extends for 80% of the length L. Coating F is located in channel E and extends over the entire length L.

[0097] Figure 3 The invention relates to a wall-flow filter, wherein coating Z is located in a porous wall and extends over the entire length L. Coating F is located in channel E and also extends over the entire length L.

[0098] Figure 4 The invention relates to a wall-flow filter, wherein coating Z is located in a porous wall and extends from a second end of the wall-flow filter substrate for 50% of the length L. Coating F is located in channel E and extends over the entire length L.

[0099] Figure 5 Including a wall-flow filter according to the invention, which is related to... Figure 4 The difference between this wall-flow filter and the conventional one is that the coating Z is located on the surface O along 50% of the length L. A The coating Y is located within the porous wall along the entire length L. The coating F is located within channel E and extends along the entire length L.

[0100] Figure 6 Including a wall-flow filter according to the invention, which is related to... Figure 4 The difference between this and the wall-flow filter is that the coating Z is on the surface O A The upper layer extends over 50% of the length L, and additionally, the coating Y extends over 50% of the length L in the porous wall, starting from the first end of the wall-flow filter substrate. The coating F is located in the channel E and extends over the entire length L.

[0101] Figure 7 This relates to a wall-flow filter according to the invention, wherein the coating Z is located on surface O. A It is located in channel A and extends for 50% of the length L. Additionally, coating Y is located on surface O. E The coating is located in channel E and extends from the first end of the wall-flow filter substrate for 50% of the length L. The coating F is located in channel E and extends from the second end of the wall-flow filter substrate for 50% of the length L.

[0102] Figure 8 The invention relates to a wall-flow filter, wherein the coating Z is located within a porous wall and extends along the entire length L. Additionally, the coating Y is located on surface O. E The coating is located in channel E and extends from the first end of the wall-flow filter substrate for 50% of the length L. The coating F is located in channel E and extends from the second end of the wall-flow filter substrate for 50% of the length L.

[0103] Figure 9 The invention relates to a wall-flow filter, wherein coating Z is located within a porous wall and extends from a second end of the wall-flow filter substrate for 50% of the length L. Additionally, coating Y is located on surface O. E The coating is located in channel E and extends from the first end of the wall-flow filter substrate for 50% of the length L. The coating F is located in channel E and extends from the second end of the wall-flow filter substrate for 50% of the length L.

[0104] Figure 10 This relates to a wall-flow filter according to the invention, wherein the coating Z is located on surface O. A The coating is located in channel A and extends for 80% of the length L from the second end of the wall-flow filter substrate. Additionally, coating Y is located in the porous wall and extends along the entire length L. Coating F is located in channel E and extends along the entire length L.

[0105] The wall-flow filter according to the invention can be manufactured by applying coatings Z, F and (if present) Y to a wall-flow filter substrate.

[0106] In this case, as specified by those skilled in the art, catalytic activity is provided by coating the wall-flow filter substrate with coating Z and (if present) coating Y.

[0107] Therefore, the term "coating" should be understood as referring to the application of catalytically active materials to a wall-flow filter substrate. It is assumed that the coating has actual catalytic functionality. In this case, coating is performed, for example, by applying a corresponding low-viscosity aqueous suspension of the catalytically active component (also known as a carrier coating) to the wall or surface of the wall-flow filter substrate according to EP1789190B1. After applying the suspension, in each case, the wall-flow filter substrate is dried and, where appropriate, calcined at an elevated temperature. The catalytically coated filter preferably has a loading of 20 g / L to 200 g / L, more preferably 30 g / L to 150 g / L (coating Z or the sum of coatings Z and Y). The optimal loading of the filter coating in the wall depends on its pore density, its wall thickness, and its porosity.

[0108] The coating F is applied to the wall-flow filter substrate, particularly by impinging a dry powder / gas aerosol onto the channel E of a dry wall-flow filter substrate that has been coated with coating Z and optional coating Y, wherein the powder contains particulate metal compounds and is specifically composed of particulate metal compounds.

[0109] By impinging dry powder / gas aerosol onto a wall-flow filter substrate that has been conventionally coated with coating Z and optionally Y, dried, and optionally calcined, a wall-flow filter according to the invention is obtained, which has excellent filtration efficiency and only a slight increase in exhaust back pressure, while also exhibiting excellent catalytic efficiency.

[0110] The wall-flow filter according to the invention, which is catalytically coated and then powder-impacted, differs from filters manufactured by ash deposition in the vehicle's exhaust system during operation. According to the invention, the catalytically active wall-flow filter substrate is selectively powder-sprayed with a specific dry powder. Therefore, the balance between filtration efficiency and exhaust back pressure can be selectively adjusted immediately from the outset. Thus, wall-flow filters where ash deposition is not defined, for example, caused by fuel combustion during driving or by means of fuel combustion in the combustor cylinder, are not included in this invention.

[0111] When dry powder / gas aerosol impacts the wall-flow filter substrate considered herein, the powder particles are deposited in the pores of the wall-flow filter substrate and optionally deposited on the surface O following the gas flow. E Above. In this method, the varying wall permeability of the wall-flow filter substrate (e.g., due to the inhomogeneity of the filter wall itself or different coating areas) causes the powder to selectively deposit in the pores of the wall or on the surface with the highest flow rate. E This effect also causes cracks or pores in the carrier coating layer, for example, to be filled by porous powder due to coating defects, resulting in more and more dust particles in the exhaust gas being retained as the exhaust gas passes through the filter. Therefore, the result is better filtration efficiency.

[0112] According to the invention, a dry wall-flow filter substrate coated with coating Z and optionally coating Y is covered with powder from its first end and in the direction of its second end (i.e., relative to the intended use, in the direction of exhaust gas flow) in such a way that the pore wall region with the strongest flow is neutralized by the porous wall and / or remains on the surface O. E A loose, inherently porous powder aggregate is applied to the filter substrate to achieve the desired increase in filtration efficiency. In this method, the formation of the inherently porous powder aggregate surprisingly results in a relatively low increase in back pressure. In a preferred embodiment, the wall-flow filter substrate is impinged with a powder / gas aerosol, such that during impingement, the powder is deposited in the pores of the porous wall and on the surface. E On top, and therein, a cohesive layer accumulates. In another preferred embodiment, the wall-flow filter is impinged with a powder / gas aerosol, such that during impingement, the powder settles in the pores of the filter wall and through these pores until it reaches the surface O. E And therefore not on surface O E An inner cohesive layer is formed on top.

[0113] To ensure that the powder / gas aerosol is deposited sufficiently well into the pores of the wall-flow filter substrate coated with coating Z and optionally coating Y, or adhered to surface O EAbove, the particle size in the aerosol should be at least smaller than the pore size of the wall-flow filter substrate. This can be measured by the average particle size (Q3 distribution, measured according to the latest ISO 13320 as of the application date) in the dried aerosol. 50 The ratio of the average pore size of the wall-flow filter after coating (measured according to the latest version of DIN 66134, application date) to the average pore size of the wall-flow filter is expressed as 0.03 to 2, preferably 0.05 to 1.43, and very particularly preferably 0.05 to 0.63. Therefore, powder particles in the aerosol that follow the gas flow can settle into the pores of the wall of the wall-flow filter substrate.

[0114] Suitable powders specifically have at least 100m 2 Specific surface area of ​​ / g and total pore volume of at least 0.3ml / g.

[0115] For powders suitable for manufacturing wall-flow filters according to the invention, optimization between the maximum possible surface area, crosslinking, and adhesive strength of the powder is advantageous. During operation in a vehicle, small particles generally follow the flow path without inertia due to their low particle relaxation time. Random "trembling motion" is superimposed on this uniform convective-driven motion. According to this theory, the maximum possible circulating surface should be provided to achieve good filtration of the wall-flow filter impacted by the powder. Therefore, the powder should have a high proportion of fine particles, because small particles provide a significantly larger surface area for the same total volume of metal compound. However, at the same time, the pressure loss must only increase slightly. This requires loose crosslinking of the powder. For coatings that enhance filtration efficiency, it is preferred to use powders with a tap density between 50 g / l and 900 g / l, preferably between 200 g / l and 850 g / l, and most preferably between 400 g / l and 800 g / l.

[0116] Aerosols consisting of gas and powder can be prepared according to the requirements of those skilled in the art or as shown below. For this purpose, the powder is typically mixed with the gas ( http: / / www.tsi.com / Aerosolgeneratoren-und- dispergierer / ; https: / / www.palas.de / de / product / aerosolgeneratorssolidparticles The mixture of gas and powder generated in this way is then advantageously fed via an airflow into the channel E of the wall-flow filter substrate.

[0117] All gases that a person skilled in the art would consider for this purpose can be used as gases for the preparation of aerosols and for introduction into wall-flow filter substrates. The use of air is particularly preferred. However, other reactive gases that produce oxidizing (e.g., O2, NO2) or reducing (e.g., H2) activity relative to the powder used may also be used. For certain powders, the use of inert gases (e.g., N2) or rare gases (e.g., He) may also prove advantageous. Mixtures of the listed gases are also conceivable.

[0118] To deposit the powder to a sufficient depth in channel E and achieve good adhesion, a certain suction power is required. Those skilled in the art can develop their own ideas in this regard through experiments with the corresponding wall-flow filters and powders. It has been found that the aerosol (powder / gas mixture) is preferably drawn through the wall-flow filter at a speed of 5 m / s to 60 m / s, more preferably 10 m / s to 50 m / s, and very particularly preferably 15 m / s to 40 m / s. This also achieves favorable adhesion of the applied powder.

[0119] The dispersion of powder in the gas used to establish the powder-gas aerosol is carried out in various ways. Preferably, the dispersion of powder is achieved by at least one or a combination of the following: compressed air, ultrasonication, sieving, "in-situ grinding", blower, gas expansion, fluidized bed. Other dispersion methods not mentioned herein are also available to those skilled in the art. In principle, those skilled in the art are free to choose the method used to prepare the powder / gas aerosol. As already described, the powder is first converted into a powder / gas aerosol by dispersion and then directed into the gas stream.

[0120] The resulting mixture of gas and powder is then introduced only into the existing airflow, which carries the finely distributed powder into channel E of the wall-flow filter substrate. This process is preferably assisted by a suction device located in a duct on the filter's outlet side. This is consistent with US8277880B. Figure 3 The apparatus shown forms a contrast, in which the powder / gas aerosol is prepared directly in the gas stream. The method according to the invention allows for a more uniform and efficient mixing of the gas stream with the powder / gas aerosol, which ultimately ensures a favorable distribution of powder particles in the filter in both the radial and axial directions, and thus helps to homogenize the powder particles and control their deposition on the filter.

[0121] When the powder impacts the wall-flow filter substrate within the meaning of this invention, the powder is dry. The powder is preferably mixed with ambient air and applied to the filter. By mixing the powder / gas aerosol with a particulate-free gas (preferably dry ambient air), the particle concentration is reduced to a level where measurable agglomeration does not occur before deposition in the wall-flow filter substrate. This preserves the particle size in the aerosol regulated during dispersion.

[0122] Figure 12 A preferred apparatus for manufacturing a wall-flow filter according to the invention is illustrated schematically. Such an apparatus is characterized by the presence of the following:

[0123] • At least one unit used to disperse powder in a gas;

[0124] • A unit used to mix dispersions with existing airflow;

[0125] • At least two filter receiving units, which are designed to allow airflow through the filter without the need for an additional gas supply;

[0126] • A suction generating unit that maintains the airflow through the filter;

[0127] Optionally, the following unit is used to generate a vortex upstream of the filter in order to prevent powder from depositing on the filter inlet plug as much as possible;

[0128] • And optionally, a unit that extracts at least one portion of the airflow from the outflow side of the suction device and adds the at least one portion of the airflow to the airflow being suctioned through the filter before powder addition.

[0129] In this preferred embodiment of the method according to the invention, such as Figure 11 As shown in the accompanying diagram, at least a portion of the airflow is extracted from the outlet side of the suction device and added back to the airflow being suctioned through the filter before powder addition. This metering adds powder to the heated airflow. The suction blower, used for the necessary pressure, generates an exhaust temperature of approximately 70°C, as the installed suction power is preferably >20kW. In an energy-optimized manner, the waste heat from the suction blower is used to heat the supply air, thereby reducing the relative humidity of the supply air. This, in turn, reduces the adhesion between particles and to the input plug. Therefore, the powder deposition process can be better controlled.

[0130] In the method of the invention for manufacturing a wall-flow filter according to the invention, the airflow is impacted by a powder / gas aerosol and drawn into the wall-flow filter substrate. This ensures that the powder is sufficiently well distributed in the airflow so that it can penetrate into the channel E. Uniform distribution of the powder in the gas / air requires thorough mixing. For this purpose, diffusers, venturi mixers, and static mixers are known to those skilled in the art. Mixing devices that prevent powder deposition on the surface of the coating system are particularly suitable for powder coating processes. Therefore, diffusers and venturi tubes are preferred for this process. Introducing dispersed powder into a rapidly rotating flow with high turbulence has also proven effective.

[0131] To achieve a favorable and uniform distribution of powder across the cross-section of the wall-flow filter substrate, the gas conveying the powder should have a piston-like flow (where the velocity is uniform across the cross-section, if possible) upon impact with the filter. This is preferably achieved through an accelerating flow upstream of the filter. As is known to those skilled in the art, such an accelerating flow results from a continuous reduction in cross-section without abrupt changes, as described by the continuity formula. Furthermore, it is known to those skilled in the art that the flow distribution thus more closely approximates a piston distribution. For targeted changes in flow rate, built-in components such as screens, rings, discs, etc., can be used below and / or above the filter.

[0132] In another advantageous design of this method, the apparatus for powder coating has one or more devices (turbulence generators, vortex generators) that, when used, allow the airflow carrying the powder / gas aerosol to vortex before impacting the filter. For example, in this regard, corresponding sieves or grids can be used, placed at a sufficient distance from the inflow side of the wall-flow filter substrate. This distance should not be too large or too small, allowing for sufficient vortexing of the airflow directly upstream of the wall-flow filter substrate. This distance can be determined by those skilled in the art through simple experiments. The advantage of this measure is explained by the fact that the powder component does not deposit on the plug of channel A, and all the powder can penetrate into channel E. Therefore, according to the invention, it is preferred that the powder vortexes before flowing into the filter in a manner that minimizes powder deposition on the plug of the wall-flow filter substrate. In aerodynamics, a turbulence generator or vortex generator refers to a device that creates an artificial disturbance to the flow. As known to those skilled in the art, vortices (especially microvortices) form at corresponding Reynolds numbers behind rods, grids, and other built-in flow disturbance components. The known examples are the Karman vortex streets (H. Benard, CRAcad. Sci. Paris. Ser. IV 147,839 (1908); 147,970 (1908); T. von Karman, Nachr. Ges. Wiss). Math.Phys.Kl.509(1911); 547(1912)) and the wake turbulence behind aircraft that can cover the roof. In the case of the invention, this effect can be particularly advantageously enhanced by a self-cleaning screen (so-called ultrasonic screen) that moves advantageously in the flow by vibration. Another method is to disturb the flow through the sound field, which excites the flow to turbulence due to pressure amplitude. These sound fields can even clean the surface of the filter without flow. The frequency can be in the range of ultrasonic to infrasonic. The latter measure is also used for pipe cleaning in large-scale technical plants.

[0133] The preferred embodiment of the wall-flow filter, with necessary modifications, also applies to this method. Reference is explicitly made to the foregoing description of the wall-flow filter in this regard.

[0134] In this invention, drying refers to the application of liquids, particularly water. Specifically, the formation of a powder suspension in a liquid for aerosolization should be avoided. Both the filter and the powder may tolerate a certain moisture content, provided that the purpose is achieved, i.e., the powder is on the surface of the porous wall and / or wall-flow filter substrate. E The finest possible deposition within the powder is not negatively affected. Typically, the powder is free-flowing and can be dispersed by energy input. The moisture content of the powder or wall-flow filter substrate when impacted by the powder should be less than 20%, preferably less than 10%, and very particularly preferably less than 5% (measured at 20°C and standard atmospheric pressure according to the latest version of ISO 11465 as of the application date).

[0135] Compared to a fresh wall-flow filter in its untreated state, the wall-flow filter according to the invention exhibits superior filtration efficiency with only a moderate increase in exhaust back pressure. The wall-flow filter according to the invention preferably shows at least 5%, preferably at least 10%, and very particularly preferably at least 20% improvement in particulate matter deposition (filtration effect) in the filter, and compared to a fresh filter coated with a catalytically active material but not treated with powder, the relative increase in exhaust back pressure of a fresh wall-flow filter is at most 40%, preferably at most 20%, and very particularly preferably at most 10%. The slight increase in back pressure may be due to the fact that the cross-section of the channel on the inlet side is not significantly reduced according to the invention by impacting the filter with powder. It is assumed that the powder itself forms a porous structure, which has a positive effect on back pressure. For this reason, the wall-flow filter according to the invention should also exhibit better exhaust back pressure than prior art filters, where powder is deposited on the wall on the filter inlet side or a conventional coating using wet techniques is selected.

[0136] Coating Z imparts excellent ternary activity to the wall-flow filter according to the invention, while optional coating Y can reduce the ignition temperature of the smoke and thus promote the burnout of the smoke.

[0137] Therefore, the present invention also relates to the use of the wall-flow filter according to the invention for reducing harmful exhaust gases from internal combustion engines. The use of the wall-flow filter according to the invention for treating exhaust gases from stoichiometric internal combustion engines, particularly gasoline-powered internal combustion engines, is preferred.

[0138] The wall-flow filter according to the invention is advantageously used in combination with at least one three-way catalyst. Particularly advantageously, the three-way catalyst is located on the inlet side of the wall-flow filter according to the invention, close to the engine. Also advantageously, the three-way catalyst is located on the outlet side of the wall-flow filter according to the invention. Furthermore, it is advantageous that the three-way catalyst is located on both the inlet and outlet sides of the wall-flow filter.

[0139] The preferred embodiments of the wall-flow filter according to the invention, with necessary modifications, are also applicable to the uses mentioned herein.

[0140] The present invention also relates to an exhaust gas purification system comprising a filter according to the invention and at least one additional catalyst. In one embodiment of the system, at least one additional catalyst is arranged upstream of the filter according to the invention. Preferably, this is a three-way catalyst, an oxidation catalyst, or a NO catalyst. x Catalyst storage. In another embodiment of the system, at least one additional catalyst is arranged downstream of the filter according to the invention. Preferably, this is a three-way catalyst, an SCR catalyst, or a NO catalyst. x A storage catalyst or ammonia slip catalyst. In another embodiment of the system, at least one additional catalyst is arranged upstream of the filter according to the invention and at least one additional catalyst is arranged downstream of the filter according to the invention. Preferably, the upstream catalyst is a ternary catalyst or an oxidation catalyst or NO. x The catalyst is stored, and the downstream catalyst is a three-way catalyst, an SCR catalyst, or a NO catalyst. x Storage catalyst or ammonia escape catalyst.

[0141] The preferred embodiments described for the wall-flow filter according to the invention, with necessary modifications, also apply to the exhaust gas purification systems mentioned herein.

[0142] Typically, the filters according to the invention are primarily used in internal combustion engines, particularly those with direct injection or intake manifold injection. These are preferably stoichiometric gasoline or natural gas engines. Preferably, these are turbocharged engines.

[0143] The requirements for gasoline particulate filters (GPFs) differ significantly from those for diesel particulate filters (DPFs). Based on particle mass, diesel engines without DPFs can have up to ten times higher particulate emissions than gasoline engines without GPFs (Maricq et al., SAE 1999-01-01530). Furthermore, gasoline engines produce significantly fewer primary particles, and their secondary particles (agglomerates) are significantly smaller than those in diesel engines. Gasoline engine emissions range from less than 200 nm (Hall et al., SAE 1999-01-3530) to 400 nm (Mathis et al., Atmospheric Environment 38 4347), with maximum values ​​in the range of approximately 60 nm to 80 nm. Therefore, for GPFs, nanoparticles must be filtered primarily through diffusion separation. For particles smaller than 300 nm, separation by diffusion (Brownian molecular motion) and electrostatic forces becomes increasingly important as the size decreases (Hinds, W.: Aerosol technology: Properties and behavior and measurement of airborne particles, Wiley, 2nd ed., 1999).

[0144] Figures 1 to 10 Different coating arrangements for wall-flow filters according to the present invention are shown, which have been described in more detail above. The following names are used herein:

[0145] (E) Inlet / outlet channel of wall flow filter

[0146] (A) Outlet / outlet channel of wall flow filter

[0147] (O E Surface formed by the inlet channel (E)

[0148] (O A ) Surface formed by the exit channel (A)

[0149] (L) Length of filter wall

[0150] (Z) Coating Z

[0151] (Y) Coating Y

[0152] (F) Coating F

[0153] Figure 11A schematic diagram of an advantageous apparatus for impinging a filter with powder is shown. Powder 420 or 421 is mixed with pressurized gas 451 passing through an atomizer nozzle 440 in a mixing chamber having an airflow 454, and is then drawn or propelled through a filter 430. The permeated particles are filtered out in an exhaust filter 400. A blower 410 provides the necessary volumetric flow rate. The exhaust gas is separated into exhaust gas 452 and hot recirculated gas 453. The hot recirculated gas 453 is mixed with fresh gas 450.

[0154] Figure 12 An optical micrograph of a wall-flow filter being bombarded by powder is shown. The image shows a top view of multiple channel walls in a region of the wall-flow filter where no catalytically active upper wall layer exists. Powder selectively deposits into and fills the pores of the walls.

[0155] Figure 13 A comparison of the back pressures of catalysts GPF1 and VGPF1 after dust loading is shown.

[0156] Figure 14 The study involved flue gas burnout tests using catalysts VGPF3, VGPF4, and VGPF5, and showed the time required for the back pressure of a flue-loaded filter to drop to 25% of the initial back pressure without flue gas (defined as p25).

[0157] The advantages of the present invention will be explained using the following examples.

[0158] Comparative Example 1: Coating Z only :

[0159] Lanthanum oxide-stabilized alumina was suspended in water along with a first oxygen storage component and a second oxygen storage component. The first oxygen storage component comprised 40 wt% cerium oxide, zirconium oxide, lanthanum oxide, and praseodymium oxide, while the second oxygen storage component comprised 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The two oxygen storage components were used in equal proportions. The weight ratio of alumina to the oxygen storage component was 30:70. The resulting suspension was then mixed with palladium nitrate and rhodium nitrate solutions under constant stirring. The resulting coating suspension was used directly to coat a commercially available wall-flow filter substrate, and the coating was introduced onto the surface O A The substrate length exceeds 80%. The total loading of the filter is 75 g / l; the total precious metal loading is 1.27 g / l, with a palladium to rhodium ratio of 5:1. The resulting coated filter is dried and then calcined. It will be referred to below as VGPF1.

[0160] According to Embodiment 1 of the present invention: a combination of coating Z and coating F :

[0161] Lanthanum oxide-stabilized alumina was suspended in water along with a first oxygen storage component and a second oxygen storage component. The first oxygen storage component comprised 40 wt% cerium oxide, zirconium oxide, lanthanum oxide, and praseodymium oxide, while the second oxygen storage component comprised 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The two oxygen storage components were used in equal proportions. The weight ratio of alumina to the oxygen storage component was 30:70. The resulting suspension was then mixed with palladium nitrate and rhodium nitrate solutions under constant stirring. The resulting coating suspension was used directly to coat a commercially available wall-flow filter substrate, and the coating was introduced onto the surface O A The substrate length exceeds 80%. The total loading of the filter is 75 g / L; the total precious metal loading is 1.27 g / L, with a palladium to rhodium ratio of 5:1. The resulting coated filter is dried and then calcined. Subsequently, the filter is impinged with dry powder / gas aerosol, in which 7 g / L of metal oxide is introduced into channel E. This is referred to below as GPF1.

[0162] The pressure loss on the two filters obtained from this method was measured on a cold-blown air test bench, VGPF1 and GPF1, to determine the pressure loss on the respective filters. This was done at room temperature and 900m. 3 At an air volumetric flow rate of / h, the back pressure of VGPF1 is 111 mbar and the back pressure of GPF1 is 122 mbar. As already described, the filter coating F only results in a modest increase in back pressure.

[0163] Furthermore, the back pressure of the two filters under soot loading was investigated. For this purpose, both filters were blackened on an engine test bench equipped with a direct-injection turbocharged engine. The final soot load was approximately 3g. Figure 13 The GPF1 according to the invention is shown, which has a higher back pressure in the clean state but a lower back pressure after dust load than the contrast filter VGPF1.

[0164] Meanwhile, the particulate filtration efficiency of the fresh VGPF1 and GPF1 filters was studied in a vehicle. For this purpose, the filters were measured close to the engine between two particulate counters in an RTS-95 (also known as RTC-aggressive) drive cycle. In both cases, the three-way catalytic converter was located upstream of the exhaust pipe, through which vehicle λ control was achieved. Here, based on the particulate values ​​from the two particulate counters, the filter nozzle GPF1 according to the invention achieved a filtration efficiency of 84%, while the contrast filter VGPF1 achieved only 55.5%. In conclusion, it can be seen that the combination of filter coating F and three-way coating Z is particularly advantageous in terms of back pressure and filtration efficiency after soot loading.

[0165] Comparative Example 2: Coating Z only

[0166] Lanthanum oxide-stabilized alumina was suspended in water along with a first oxygen storage component and a second oxygen storage component. The first oxygen storage component comprised 40 wt% cerium oxide, zirconium oxide, lanthanum oxide, and praseodymium oxide, while the second oxygen storage component comprised 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The two oxygen storage components were used in equal parts. The weight ratio of alumina to the oxygen storage component was 30:70. The resulting suspension was then mixed with a palladium nitrate solution and a rhodium nitrate solution under constant stirring. The resulting coating suspension was directly applied to a commercially available wall-flow filter substrate, introducing the coating into the porous filter wall over 100% of the substrate length. The total loading of the filter was 75 g / L; the total precious metal loading was 1.24 g / L, with a palladium to rhodium ratio of 6:1. The resulting coated filter was dried and then calcined. This is hereinafter referred to as VGPF2.

[0167] Embodiment 2 of the present invention: Combination of coating Z and coating F :

[0168] Lanthanum oxide-stabilized alumina was suspended in water with a first oxygen storage component and a second oxygen storage component. The first oxygen storage component contained 40 wt% cerium oxide, zirconium oxide, lanthanum oxide, and praseodymium oxide, and the second oxygen storage component contained 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The two oxygen storage components were used in equal parts. The weight ratio of alumina to oxygen storage components was 30:70. The resulting suspension was then mixed with a palladium nitrate solution and a rhodium nitrate solution under constant stirring. The resulting coating suspension was directly applied to a commercially available wall-flow filter substrate, introducing the coating into the porous filter wall over 100% of the substrate length. The total loading of the filter was 75 g / L; the total precious metal loading was 1.24 g / L, with a palladium to rhodium ratio of 6:1. The resulting coated filter was dried and then calcined. Subsequently, the filter was impinged with a dry powder / gas aerosol, in which 10 g / L of metal oxide was introduced into channel E. This is referred to below as GPF2.

[0169] The particulate filtration efficiency of two filters, VGPF2 and GPF2, was investigated in a vehicle. For this purpose, the filters were measured close to the engine between two particulate counters during a WLTP drive cycle. In both cases, a three-way catalytic converter was located upstream of the exhaust pipe, through which vehicle λ control was achieved. Based on the particulate values ​​from the two particulate counters, the filter GPF2 according to the invention achieved an 85% filtration efficiency, while the contrast filter VGPF2 only achieved 65%.

[0170] Furthermore, filters VGPF2 and GPF2 were aged together during the engine test bench aging process. This aging process included an over-limit cutoff aging process, with an exhaust gas temperature of 950°C (maximum bed temperature of 1030°C) before the catalyst inlet. The aging time was 76 hours (see Motortechnische Zeitschrift, 1994, 55, 214–218). The catalytically active particulate filters under aging conditions were then tested on the engine test bench in so-called “ignition test” and “λ sweep test” to compare their catalytic activity. In the ignition test, ignition behavior was determined under stoichiometric exhaust gas composition with a constant average air-to-fuel ratio of λ (λ = 0.999 and ±3.4% amplitude).

[0171] Table 1 below contains temperature T 50 At these temperatures, 50% of the considered component is converted respectively.

[0172] VGPF2 366 373 372 GPF2 366 373 373

[0173] Table 1

[0174] The dynamic conversion behavior of the particulate filter was determined by a λ sweep frequency test within the range of λ = 0.99–1.01 at a constant temperature of 510 °C. In this case, the amplitude of λ was ±6.8%. Table 2 shows the conversion rates at the intersection of the CO and NOx conversion curves, as well as the associated HC conversion rates of the aged particulate filter.

[0175] VGPF2 93 92 GPF2 92 93

[0176] Table 2

[0177] These tests clearly demonstrate that the filter coating F is particularly suitable for significantly increasing the filtration efficiency of the filter GPF2 according to the present invention without affecting the catalytic activity of the filter.

[0178] Comparative Example 3: Coating Z only

[0179] Lanthanum oxide-stabilized alumina was suspended in water along with a first oxygen storage component and a second oxygen storage component. The first oxygen storage component comprised 40 wt% cerium oxide, zirconium oxide, lanthanum oxide, and praseodymium oxide, while the second oxygen storage component comprised 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The two oxygen storage components were used in equal proportions. The weight ratio of alumina to the oxygen storage component was 30:70. The resulting suspension was then mixed with palladium nitrate and rhodium nitrate solutions under constant stirring. The resulting coating suspension was used directly to coat a commercially available wall-flow filter substrate, and the coating was introduced onto the surface O AThe substrate length exceeds 60%. The total loading of the filter is 75 g / l; the total precious metal loading is 0.88 g / l, with a palladium to rhodium ratio of 4:1. The resulting coated filter is dried and then calcined. It will be referred to below as VGPF3.

[0180] Comparative Example 4: Coating Z only

[0181] Lanthanum oxide-stabilized alumina was suspended in water along with a first oxygen storage component and a second oxygen storage component. The first oxygen storage component comprised 40 wt% cerium oxide, zirconium oxide, lanthanum oxide, and praseodymium oxide, while the second oxygen storage component comprised 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The two oxygen storage components were used in equal proportions. The weight ratio of alumina to the oxygen storage component was 30:70. The resulting suspension was then mixed with solutions of palladium nitrate, platinum nitrate, and rhodium nitrate under constant stirring. The resulting coating suspension was used directly to coat a commercially available wall-flow filter substrate, and the coating was introduced onto the surface O A The substrate length exceeds 60%. The total loading of the filter is 75 g / L; the total precious metal loading is 0.88 g / L, with a platinum, palladium, and rhodium ratio of 92:108:50. The resulting coated filter is dried and then calcined. It will be referred to below as VGPF4.

[0182] Comparative Example 5: Combination of Coating Y and Coating Z :

[0183] Stabilized alumina was suspended in water. The resulting suspension was then mixed with a palladium nitrate solution and a platinum nitrate solution under constant stirring. The resulting coating suspension was directly applied to a commercially available wall-flow filter substrate, introducing the coating into the porous filter wall along 100% of the substrate length. The total loading of the filter was 10 g / L; the total precious metal loading was 0.35 g / L, with a palladium to rhodium ratio of 12:1. The resulting coated filter was dried and then calcined. Alumina stabilized with lanthanum oxide was then suspended in water with a first oxygen storage component and a second oxygen storage component. The first oxygen storage component contained 40 wt% cerium oxide, zirconium oxide, lanthanum oxide, and praseodymium oxide, and the second oxygen storage component contained 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The two oxygen storage components were used in equal parts. The weight ratio of alumina to oxygen storage components was 30:70. The resulting suspension was then mixed with a palladium nitrate solution and a rhodium nitrate solution under constant stirring. The resulting coating suspension was directly used to coat commercially available wall-flow filter substrates, and the coating was introduced onto the surface O A The substrate length exceeds 60%. The total loading of the filter is 85 g / l; the total precious metal loading is 0.88 g / l, with a platinum, palladium, and rhodium ratio of 92:108:50. The resulting coated filter is dried and then calcined. It will be referred to below as VGPF5.

[0184] Filters VGPF3, VGPF4, and VGPF5, manufactured in this manner, were initially loaded with a limited amount of particulate matter and subsequently studied on an engine test bench in particulate matter burnout tests at a constant temperature of 450°C upstream of the catalyst inlet with a lean exhaust gas composition to determine their particulate matter oxidation characteristics. It was found that the combination of coatings Y and Z in VGPF5 was optimal for the complete regeneration of the particulate filter. The time required for the back pressure of the particulate-loaded filter to drop to 25% of its initial back pressure without particulate matter (defined as p25) was considered. Figure 14 As can be seen, the combination of coating Y and coating Z in VGPF5 reaches the p25 value after about 1700 seconds, while VGPF3 and VGPF4 reach the p25 value after only 4100 seconds and 2250 seconds, respectively.

[0185] Comparative Example 6: Combination of Coating Y and Coating Z :

[0186] Stabilized alumina was suspended in water. The resulting suspension was then mixed with a palladium nitrate solution and a platinum nitrate solution under constant stirring. The resulting coating suspension was directly applied to a commercially available wall-flow filter substrate, introducing the coating into the porous filter wall over 100% of the substrate length. The total loading of the filter was 10 g / L; the total precious metal loading was 0.28 g / L, with a palladium to rhodium ratio of 12:1. The resulting coated filter was dried and then calcined. Next, alumina stabilized with lanthanum oxide was suspended in water with an oxygen storage component comprising 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The weight ratio of alumina to the oxygen storage component was 55:45. The resulting suspension was then mixed with a palladium nitrate solution and a rhodium nitrate solution under constant stirring. The resulting coating suspension was directly applied to a commercially available wall-flow filter substrate, introducing the coating into the surface O A The substrate length exceeds 80%. After the second step, the total loading of the filter is 60 g / l; the total precious metal loading is 0.48 g / l, with a palladium to rhodium ratio of 738:262:359. The resulting coated filter is dried and then calcined. It will be referred to below as VGPF6.

[0187] According to Embodiment 3 of the present invention: a combination of coating Y with coating Z and coating F :

[0188] Stabilized alumina was suspended in water. The resulting suspension was then mixed with a palladium nitrate solution and a platinum nitrate solution under constant stirring. The resulting coating suspension was directly applied to a commercially available wall-flow filter substrate, introducing the coating into the porous filter wall over 100% of the substrate length. The total loading of the filter was 10 g / L; the total precious metal loading was 0.28 g / L, with a palladium to rhodium ratio of 12:1. The resulting coated filter was dried and then calcined. Next, alumina stabilized with lanthanum oxide was suspended in water with an oxygen storage component comprising 24 wt% cerium oxide, zirconium oxide, lanthanum oxide, and yttrium oxide. The weight ratio of alumina to the oxygen storage component was 55:45. The resulting suspension was then mixed with a palladium nitrate solution and a rhodium nitrate solution under constant stirring. The resulting coating suspension was directly applied to a commercially available wall-flow filter substrate, introducing the coating into the surface O A The substrate length exceeds 80%. After the second step, the total loading of the filter is 60 g / L; the total precious metal loading is 0.48 g / L, with a palladium to rhodium ratio of 738:262:359. The resulting coated filter is dried and then calcined. Subsequently, the filter is impinged with dry powder / gas aerosol, in which 4 g / L of metal oxide is introduced into channel E. This is referred to below as GPF3.

[0189] The particulate filtration efficiency of two filters, VGPF6 and GPF3, was investigated in a vehicle. For this purpose, the filters were measured close to the engine between two particulate counters during a WLTP drive cycle. In both cases, a three-way catalytic converter was located upstream of the exhaust pipe, through which vehicle λ control was achieved. Here, based on the particulate values ​​from the two particulate counters, the filter GPF3 according to the invention achieved a filtration efficiency of 96%, while the contrast filter VGPF6 achieved only 71%.

[0190] Furthermore, the pressure loss of the two filters obtained in their fresh state was measured on a cold-blown air test bench to determine the pressure loss on each filter. This was done at room temperature and 300m. 3 At an air volumetric flow rate of / h, the back pressure of VGPF6 is 69 mbar and that of GPF3 is 122 mbar. As already described, the filter coating F only results in a modest increase in back pressure.

[0191] Furthermore, the back pressure of the two filters under soot load was investigated. For this purpose, both filters were blackened on an engine test bench equipped with a direct-injection turbocharged engine. For a soot load of 3g, the GPF3 according to the invention, although exhibiting a higher back pressure under clean conditions, had a lower back pressure than the comparative filter VGPF6 (Table 3).

[0192] VGPF6 69 244 GPF3 122 205

[0193] Table 3

[0194] In summary, it can be seen that the additional regenerable coating Y can be optionally combined with the filter coating F and the ternary coating Z, wherein the advantages in back pressure behavior after dust load and in filtration efficiency are still retained compared with the filter without coating F.

Claims

1. A wall-flow filter for removing particulate matter from exhaust gases of an internal combustion engine, the wall-flow filter comprising a wall-flow filter substrate of length L and coatings Z and F, which are different from each other. The wall-flow filter substrate has channels E and A, which extend parallel to each other between a first end and a second end of the wall-flow filter substrate, are separated by porous walls, and respectively form surface O. E and O A And wherein channel E is closed at the second end and channel A is closed at the first end, and The coating Z is located in the porous wall and / or on the surface O. A On, but not on the surface O E Above, and contains palladium and / or rhodium as well as cerium / zirconium mixed oxide, Its features are, The coating F is located in the porous wall and / or on the surface O. E On, but not on the surface O A It contains particulate metal compounds but no precious metals. The wall-flow filter substrate has a coating Y that differs from coatings Z and F. Coating Y comprises platinum, palladium, or platinum and palladium, does not contain rhodium and cerium / zirconium mixed oxides, and is located within the porous wall but not on the surface O. A superior; The wall-flow filter has a coating F with an increasing concentration gradient in the longitudinal direction of the filter from the first end to the second end of the filter.

2. The wall-flow filter according to claim 1, characterized in that, The coating Z is located on the surface O of the wall-flow filter substrate. A It extends from the second end of the wall-flow filter substrate to 50% to 90% of the length L.

3. The wall-flow filter according to claim 1, characterized in that, The coating Z is located in the porous wall of the wall-flow filter substrate and extends from the first end of the wall-flow filter substrate to 50% to 100% of the length L.

4. The wall-flow filter according to claim 1, characterized in that, The coating Z contains palladium and rhodium.

5. The wall-flow filter according to claim 1, characterized in that, The coating Z does not contain platinum.

6. The wall-flow filter according to claim 1, characterized in that, The cerium / zirconium mixed oxide of the coating Z contains one or more rare earth metal oxides.

7. The wall-flow filter according to claim 6, characterized in that, The rare earth metal oxides are lanthanum oxide, yttrium oxide, praseodymium oxide, neodymium oxide and / or samarium oxide.

8. The wall-flow filter according to claim 1, characterized in that, The coating Z comprises lanthanum-stabilized aluminum oxide, rhodium, palladium or palladium and rhodium, and a cerium / zirconium / rare earth metal mixed oxide containing yttrium oxide and lanthanum oxide as rare earth metal oxides.

9. The wall-flow filter according to claim 1, characterized in that, The coating Z comprises lanthanum-stabilized aluminum oxide, rhodium, palladium or palladium and rhodium, and a cerium / zirconium / rare earth metal mixed oxide containing praseodymium oxide and lanthanum oxide as rare earth metal oxides.

10. The wall-flow filter according to claim 1, characterized in that, The coating F is composed of one or more particulate metal compounds.

11. The wall-flow filter according to claim 10, characterized in that, The particulate metal compound of the coating F is cerium oxide, titanium dioxide, zirconium dioxide, silicon dioxide, aluminum oxide, or a mixture or mixed oxide thereof.

12. The wall-flow filter according to claim 1, characterized in that, The coating Y extends over a length of 50% to 100% of the length L.

13. A method for manufacturing a wall-flow filter according to any one of claims 1 to 11, characterized in that, The channel E of the dry wall-flow filter substrate, which has been coated with coating Z and optional coating Y, is impacted by a dry powder / gas aerosol, wherein the powder contains particulate metal compounds.

14. Use of the wall-flow filter according to any one of claims 1 to 11 for reducing harmful exhaust gases from an internal combustion engine.

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